1. Field of the Invention
This invention relates to an engine idle control, and more particularly to an improved idle control that is suitable for marine engines.
2. Description of Related Art
An engine has an air induction system to deliver an air charge to each combustion chamber of the engine. The air induction system may comprise a main passage in which a throttle valve is provided and an bypass passage that bypasses the throttle valve for supplying an idle air charge to the combustion chamber when the throttle valve is generally closed. In order to restraining fluctuations in idle engine speeds caused by dispersion of engine loads and also air charge amounts, conventionally the bypass passage is provided with a valve for adjusting an idle air charge passing therethrough. The adjusting valve is controlled by a control device based upon a difference between an actual idle speed and an aimed idle speed that is preset in the control device.
The engine can be incorporated in an outboard motor for propelling an associated watercraft. The watercraft is occasionally required to move forward in an extremely slow speed, i.e., a xe2x80x9ctrolling speed,xe2x80x9d for the occupant of the watercraft to fish. The trolling speed generally corresponds to an idle speed of the engine because it is obtained when a transmission is shifted to the forward position under the idle speed condition. However, some fishing techniques require the watercraft to move forward at a speed slower than the idle speed.
If the engine were not to be provided with the control device, it would be quite easy to decrease the idle speed. The occupant would only need to adjust an idle opening of the throttle valve so that a desired trolling speed is obtained. A control device of an engine, however, interferes with the closing operation of the throttle valve. That is, since the aimed idle engine speed is preset in the control device, even though the occupant adjusts the opening of the throttle valve, the control device precisely controls the adjusting valve in the bypass passage to meet with the aimed idle engine speed. As a result, the occupant cannot change the idle speed in response to the various usage inasmuch as a conventional idle speed control device which is not electronically controlled.
A need therefore exists for an improved idle speed control device that can change an aimed idle engine speed that is preset therein in response to various needs of an occupant or user.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body defining at least one cylinder bore in which a piston reciprocates to rotate a cranks haft. A cylinder head is affixed to an end of the cylinder and defines a combustion chamber with the cylinder bore and the piston. An air induction system delivers an air charge to the combustion chamber. The air induction system includes a main passage having a throttle device therein and a bypass passage arranged to bypass the throttle valve for supplying an idle air charge to the combustion chamber when the throttle valve is generally closed. The bypass passage has an flow regulator therein to govern the idle air charge flow. A speed sensor is arranged to sense engine speed. A controller is connected to the speed sensor and to the flow regulator. The controller controls the flow regulator in the bypass passage to reduce a difference between the engine speed sensed by the speed sensor and an aimed idle speed that is preset in the controller. The controller also includes an idle adjuster to change the preset aimed idle speed.
In accordance with another aspect of the present invention, an idle control system is provided for an internal combustion engine. The engine has at least one combustion chamber. An air induction passage delivers an air charge to the combustion chamber. A bypass passage bypasses the air induction passage under the idle condition of the engine. The bypass passage includes means for adjusting an amount of the air charge passing therethrough. The idle speed control system comprises a speed sensor to sense an engine speed. Means are provided for controlling the adjusting means to reduce a difference between an actual engine speed sensed by the speed sensor and an aimed idle engine speed preset in the control system. Means are provided for changing the aimed idle engine speed.
In accordance with a further aspect of the present invention, a method of operating an internal combustion engine is provided. The engine has at least one combustion chamber. An air induction passage delivers an air charge to the combustion chamber. A bypass passage bypasses a portion of the air induction passage under the idle condition of the engine. The bypass passage includes a flow regulator to adjust an amount of the air charge passing therethrough. The method involves establishing an idle engine speed and sensing an actual engine speed. The flow regulator is controlled to reduce the difference between the actual engine speed and the aimed idle speed. The aimed idle speed is changed to vary the engine speed at idle in order to suit certain applications of the engine. For example, the engine speed can be lowered to a trolling speed wherein the engine is employed in an outboard motor.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.